Photoinitiators, in particular mono- and bisacylphosphane oxides, bearing further functionalized substituents, have attracted significant commercial attention since photoinitiators which are tunable with respect to the wavelength at which photoinduced cleavage occurs or which are linkable to other additives, such as sensitizers, stabilizers or surface active agents in order to avoid migration e.g., in food packaging, are highly desirable.
Many approaches to achieve these goals have been published during the last decade.
EP 1 135 399 A describes a process for the preparation of mono- and bisacylphosphanes and their respective oxides and sulfides the process comprising the steps of reacting substituted monohalophosphanes or dihalophosphanes with an alkali metal or a combination of magnesium and lithium, where appropriate in the presence of a catalyst, further reacting the resulting metallated phosphanes with carboxylic acid halides, and finally oxidizing the resulting mono- or bisacylphosphanes with sulfur or oxygen transferring oxidants.
WO05/014605A describes the preparation of bisacylphosphanes via a process comprising the steps of first reacting monohalophosphanes or dihalophosphanes with an alkali metal in a solvent in the presence of a proton source, and then reacting the phosphanes obtained thereby with carboxylic acid halides.
WO2006/056541A describes a process for the preparation of bisacylphosphanes, the process comprising the steps of reducing elemental phosphorous or phosphorous trihalides P(Hal)3 with sodium to obtain sodium phosphide Na3P, then adding sterically bulky alcohols to obtain sodium phosphide NaPH2, reacting said sodium phosphide with two equivalents of an carboxylic acid halide to obtain sodium bisacylphosphides, and finally reacting said sodium bisacylphosphides with electrophilic agents to obtain bisacylphosphanes.
WO2006/074983A describes a process for the preparation of bisacylphosphanes by first catalytically reducing monochloro- or dichlorophosphines with hydrogen at a temperature of from 20 to 200° C. under pressure in the presence of a tertiary aliphatic amine or an aromatic amine in an aprotic solvent to obtain the corresponding halogen-free phosphanes, and subsequently reacting said phosphanes with carboxylic acid halides to obtain mono- or bisacylphosphanes.
However, for the variation of the non-acyl substituent(s) at the phosphorous atom the aforementioned processes either require                the initial employment of an organic mono- or dihalophosphane already bearing such substituent(s) in a first reduction or metallation step, which significantly diminishes the variability of possible substitution patterns, or        if e.g., sodium phosphides NaPH2 are employed, the use of electrophilic compounds bearing a reactive halogen functionality at the substituent to be introduced, which renders such processes commercially less attractive.        